Air filter



FIG. 1 shows a front view of an air filter showing my new design;

FIG. 2 shows a rear view thereof;

FIG. 3 shows a right side view thereof;

FIG. 4 shows a left side view thereof;

FIG. 5 shows a top view thereof;

FIG. 6 shows a bottom view thereof; and,

FIG. 7 shows a top, front and right side perspective view thereof.

The broken lines depict portions of the air filter that form no part of the claimed design. 

The ornamental design for an air filter, as shown and described. 